10,230 research outputs found
Analytical Hartree-Fock gradients for periodic systems
We present the theory of analytical Hartree-Fock gradients for periodic
systems as implemented in the code CRYSTAL. We demonstrate how derivatives of
the integrals can be computed with the McMurchie-Davidson algorithm. Highly
accurate gradients with respect to nuclear coordinates are obtained for systems
periodic in 0,1,2 or 3 dimensions.Comment: accepted by International Journal of Quantum Chemistr
A technique for breaking ice in the path of a ship
A technique is described for breaking ice in the path of a ship. A laser is placed on the bow of the ship with apparatus to scan the ice in the path of the ship with the laser beam. The beam cuts or shatters the ice, enabling the ship to break the ice in its path
Hybrid functionals within the all-electron FLAPW method: implementation and applications of PBE0
We present an efficient implementation of the PBE0 hybrid functional within
the full-potential linearized augmented-plane-wave (FLAPW) method. The
Hartree-Fock exchange term, which is a central ingredient of hybrid
functionals, gives rise to a computationally expensive nonlocal potential in
the one-particle Schroedinger equation. The matrix elements of this exchange
potential are calculated with the help of an auxiliary basis that is
constructed from products of FLAPW basis functions. By representing the Coulomb
interaction in this basis the nonlocal exchange term becomes a Brillouin-zone
(BZ) sum over vector-matrix-vector products. We show that the Coulomb matrix
can be made sparse by a suitable unitary transformation of the auxiliary basis,
which accelerates the computation of the vector-matrix-vector products
considerably. Additionally, we exploit spatial and time-reversal symmetry to
identify the nonvanishing exchange matrix elements in advance and to restrict
the k summations for the nonlocal potential to an irreducible set of k points.
Favorable convergence of the self-consistent-field cycle is achieved by a
nested density-only and density-matrix iteration scheme. We discuss the
convergence with respect to the parameters of our numerical scheme and show
results for a variety of semiconductors and insulators, including oxide
materials, where the PBE0 hybrid functional improves the band gaps and the
description of localized states in comparison with the PBE functional.
Furthermore, we find that in contrast to conventional local
exchange-correlation functionals ferromagnetic EuO is correctly predicted to be
a semiconductor.Comment: 15 pages, 6 figures, 2 table
The Finite Size Error in Many-body Simulations with long-Ranged Interactions
We discuss the origin of the finite size error of the energy in many-body
simulation of systems of charged particles and we propose a correction based on
the random phase approximation at long wave lengths. The correction comes from
contributions mainly determined by the organized collective oscillations of the
interacting system. Finite size corrections, both on kinetic and potential
energy, can be calculated within a single simulation. Results are presented for
the electron gas and silicon.Comment: 4 pages, 4 figures, submitted to PRL; corrected typo
PILOT: design and capabilities
The proposed design for PILOT is a general-purpose, wide-field 1 degree 2.4m,
f/10 Ritchey-Chretien telescope, with fast tip-tilt guiding, for use 0.5-25
microns. The design allows both wide-field and diffraction-limited use at these
wavelengths. The expected overall image quality, including median seeing, is
0.28-0.3" FWHM from 0.8-2.4 microns. Point source sensitivities are estimated.Comment: 4 pages, Proceedings of 2nd ARENA conference 'The Astrophysical
Science Cases at Dome C', Potsdam, 17-21 September 200
A simple, efficient, and general treatment of the singularities in Hartree-Fock and exact-exchange Kohn-Sham methods for solids
We present a general scheme for treating the integrable singular terms within
exact exchange (EXX) Kohn-Sham or Hartree-Fock (HF) methods for periodic
solids. We show that the singularity corrections for treating these
divergencies depend only on the total number and the positions of k-points and
on the lattice vectors, in particular the unit cell volume, but not on the
particular positions of atoms within the unit cell. The method proposed here to
treat the singularities constitutes a stable, simple to implement, and general
scheme that can be applied to systems with arbitrary lattice parameters within
either the EXX Kohn-Sham or the HF formalism. We apply the singularity
correction to a typical symmetric structure, diamond, and to a more general
structure, trans-polyacetylene. We consider the effect of the singularity
corrections on volume optimisations and k-point convergence. While the
singularity corrections clearly depends on the total number of k-points, it
exhibits a remarkably small dependence upon the choice of the specific
arrangement of the k-points.Comment: 24 pages, 5 Figures, re-submitted to Phys. Rev. B after revision
Two arch criteria of the ilium for sex determination of immature skeletal remains: A test of their accuracy and an assessment of intra- and inter-observer error
Although the assignment of sex to immature skeletal remains is considered problematic, some traits have been considered useful for both forensic and bioarchaeological applications. One such trait is the arch criterion found in subadult ilia, which is defined relative to the greater sciatic notch-auricular surface area. In adults, the composite arch has also been described in relation to this area and has proven relatively successful in sex determination. This study offers an examination of the accuracy of the arch criterion and the composite arch in determining the sex of subadult skeletal remains, and an assessment of intra- and inter-observer scoring error. A sample of 97 skeletons of known sex and age (<15 years) from the Lisbon collection (Portugal) were selected and the traits were scored by three observers on orthogonal photos of each ilium. In general the agreement within (67.7-88.5%) and between (50.5-76.3%) examiners was poor and overall accuracy (26.7-52.6%) did not meet the expectations of that reported in previous studies. The authors suggest that this derives from great variation in morphology, difficulties in interpreting criteria and possibly a lack of association between the expression of the traits and sex. Careful examination of sex-related morphology in the immature skeleton and additional blind tests of so-called useful traits should continue to be carried out.http://www.sciencedirect.com/science/article/B6T6W-4S2VFY1-1/1/207963d293280dcfbc0bec484ebcc10
Band structures of rare gas solids within the GW approximation
Band structures for solid rare gases (Ne, Ar) have been calculated using the
GW approximation. All electron and pseudopotential ab initio calculations were
performed using Gaussian orbital basis sets and the dependence of particle-hole
gaps and electron affinities on basis set and treatment of core electrons is
investigated. All electron GW calculations have a smaller particle-hole gap
than pseudopotential GW calculations by up to 0.2 eV. Quasiparticle electron
and hole excitation energies, valence band widths and electron affinities are
generally in very good agreement with those derived from optical absorption and
photoemission measurements.Comment: 7 pages 1 figur
Jastrow correlation factor for atoms, molecules, and solids
A form of Jastrow factor is introduced for use in quantum Monte Carlo
simulations of finite and periodic systems. Test data are presented for atoms,
molecules, and solids, including both all-electron and pseudopotential atoms.
We demonstrate that our Jastrow factor is able to retrieve a large fraction of
the correlation energy
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